Bright dip



Patented Apr. 18, 1.939

BRIGHT nrr Floyd F. Oplinger, Niagara Falls, N. Y., assignor, by mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware E No Drawing. Continuation of application Serial No. 734,703, July 11, 1934. This application July 28, 1934, Serial No. 737,406

10 Claims.

stain. oxidizing agents alone, similarly, are not satisfactory brighteners. Apparently, there is some synergetic action between the acid and brightening of electrodeposited cadmium with oxidizing agent which causes the mixture to acidified solutions of oxidizing agents. This inexercise an unexpected passivating and bright- 5 vention is, moreover, directed to the solutions ening action. used in such processes. The oxidizing agent may be acidified with any The cadmium plating processes now in use desired material of acid reaction. I preferto use frequently produce plated articles which are sulfuric acid, both because it is cheaper and stained and are not of a uniformly bright finish. because it leads to superior results. I may, how- 10 With articles of very irregular shape some areas ever, use inorganic acids such as hydrochloric, may be somewhat dull so that the piece does not phgphoric, carbonic, etc., or organic acidssuch have as uniformly a bright and lustrous finish as as lactic, acetic, citric, etc. Very weak acids such is desirable. Electrodeposited cadmium, moreas carbonic and hypo'izhlorous are none too satisl5 over, displays the very disadvantageous property factory, for, while they operate as do stronger 16 of staining easily, especially when touched by acids, they are effective to a much smaller dethe fingers. This renders a plated article very gree. Some acids, such as lgglriodiaaciiare not difficult to handle without seriously damaging its economical, when used with hydrogen peroxide, appearance. for the reason that they pause rather rapid de;

20 It has previously been proposed to treat cadcomposition of the peroxide and so shorten the 20 mium plate with dilute oxidizing acids, but this life of the bright dip. While I may use any acid, proposed treatment has the disadvantage that a organic or inorganic, I prefer to use acetic acid very considerable portion of the cadmium is disor a mineral acid such as hydrochloric or sulsolved. An oxidizing acid, even at the minimum furic.

effective concentration, may thus seriously dam- Jnstead of using acids, I may acidify a solution 25 age the finish, Certain oxidizing acids also are of an oxidizing agent with an acidulous organic unsatisfactory as they cause the formation of a or inorganic salt. As examples of such acidulous colored film which is removable with great difiisalts I may mention ferric chloride, cupric sulculty. Another disadvantage of oxidizing acid fate, potassium per sulfate, cupric chloride,

bright dips appears in the treatment of cadmium sodium bis ul fate, potassium acid phthalate, etc. 80

plated iron or steel over which nickel is to be While any acidulous salt may be employed, cerplated. When certain oxidizing acids are emtain ones, such as iron or copper salts are none ployed as bright dips a subsequently applied too satisfactory when used with hydrogen pernickel plate will not adhere properly. oxide, because they accelerate its decomposition.

I have found that the use of acidified solutions The amount of acidulous material used with of oxidizing agents, and particularly acidified an oxidizing agent is of the greatest importance. hydrogen peroxide solutions, as bright dips over- If the ratio of hydrogen peroxide, for instance,

? come the disadvantages encountered with prior to the acidulous material be too small, the action 1 art bright dips. Unlike solutions of oxidizing of the dip will be typical of a direct acid etch.

acids, my bright dips do not dissolve a cad- One must be careful, then, to use less acidulous 40 mium plate to such an extent as to damage the material than will cause an etching of the cadflnish, and they do not stain or discolor the mium plate being bright dipped. When sulfuric work. Cadmium plate bright dipped by my acid and hydrogen peroxide are used, for inprocesses may be nickel plated quite successfully, stance, the ratio of H202 (by weight) to H2804 the nickel adhering in a very' satisfactory man- (by weight) should not be less than about one 45 ner. to one. If a ratio substantially below one to one An outstanding advantage gained through the is used the dip will exercise a deleterious etching use of acidified solutions of oxidizing agents is action on a cadmium plate. The other acidulous -that cadmium plate treated therewith becomes materials are used in corresponding amounts.

passive. By reason of thisipassivity the plate The concentration of acidulous material and 50 is no longer sensitive to staining and may be oxidizing agent may be varied at will. If a dilute handled freely. solution be used, a longer time will be required Acids alone, in the small concentrations used, to accomplish the desired passivating and brightdo not display a. satisfactory brightening action, ening action than if a more concentrated solution though they may removega slight amount of be used. It is noted that for the best results 55 a higher ratio of oxidizing agent to acidulous material should be used in dilute solutions than in more concentrated ones. In general, I may state that the ratio of oxidizing agent to acidic material is such that at a suitable dilution no deleterious etching action occurs during the exposure required to brighten a cadmium plate;

The following example illustrates a preferred process and bright dip of my invention:

Emample.--A U-shaped article, cadmium plated in known manner, was selected for test purposes. This form, like objects of irregular shape generally, tends to be dull in the recessed portions. After the article was'plated it was rinsed in water and then dipped for about seconds into a bright dip comprising 6 ounces of 100 volume H202 solution, one ounce of concentrated H2804, and a gallon of Water. 0n removal from the bright dip the article was carefully washed and dried. The resulting article was passive to staining and had a lustrous, uniformly bright finish,

the recessed portions being uniform in appearance with the rest of the article. It is noted that the ratio of H202 (by weight) to H2804 (by weight) was about 1.6 to 1.

My bright dip has about as long a life as other commercial bright dips, but care must be exercised lest some agent or condition be encountered which will accelerate decomposition.

I prefer to use relatively pure acids, as impurities such as are commonly found in commercial acids may cause decomposition of the bright dip.

The solution is preferably shipped and used inglass, glazed stoneware, hard rubber, or stainless steel receptacles. If lead, Monel metal, fiber, and similar materials are used to contain my peroxide bright dip a more rapid decomposition occurs.

7 I may, if desired, add a small amount of a ,2" {L known stabilizer for peroxide. The nature and use eTstathizers'reweu"known to the trade and need not be described in detail. I have found small amounts of alcohoL sodium pyrophosphate ,(L my; and sodium stannate, glyc'erine, etc., quite satisfactory.

The peroxide bright dip may be sold in the form of a relatively concentrated solution of peroxide and acidulous material and a buyer can dilute the product to the desired extent. of

course, it can be'sold as a relatively dilute solution or it can be made up at the place of use.

While the above example mentions only hydrogen peroxide as an oxidizing agent, it is obvious that other per-oxygen compounds may be em-l ployed. In general, I may use any oxidizing agent and I do not intend to be limited to the use of hydrogen peroxide.

While I have shown numerous specific conditions and limitations I do not intend to be restricted thereby, the scope of my invention appearing from the following claims.

This-application is a continuation of my 00- pending application Ser. No. 734,703, filed July 11, 1934.

I claim:

1. A composition for passivating and brightening cadmium comprising hydrogen peroxide and sulfuric acid, the ratio of peroxide to acid being about one and six tenths to one.

2. In a process for the passivation and brightening of cadmium the step comprising subjecting the cadmiumto the action of a bright dip comprising hydrogen peroxide and a substance of acid reaction.

3. In a process for the passivation and bright- V ening of cadmium the step comprising subjecting the cadmium to the action of a bright dip comprising hydrogen peroxide and an acidic material selected from the group consisting of mineral acids and acidulous mineral acid salts. I

4. In a process for the passivation and brightening of cadmium the step comprising subjecting.

the cadmium to the action of a bright dip comprising hydrogen peroxide and sulfuric acid.

5. In a process for the passivation and brightening of cadmium the step comprising subjecting the cadmium to the action of a bright dip comprising hydrogen peroxide and sulfuric acid, the ratio of the peroxide to acid being no less than about one to one.

6. In a process for the passivation and brightening of cadmium the step comprising subjecting the cadmium to the action of a bright dip comprising hydrogen peroxide and hydrochloricacid.

10. In a process for the passivation and brightening of cadmium the step comprising subjecting the cadmium to the action of a bright dip comprising hydrogen peroxide and sulfuric acid, the ratio of peroxide to acid being about 1.6 to 1.

FLOYD F. OPLINGER. 

